Conventional concrete-coated steel pipes comprise a steel cylinder having a layer of concrete disposed over an outside surface of the steel cylinder. A technique used for making such conventional concrete-coated steel pipes is by weight coating method, which involves placing the steel cylinder onto a conveyor belt, and helically winding concrete and wire mesh around an outer surface of the steel cylinder. The resulting concrete-coated steel pipe thereby comprises a concrete layer disposed around the steel cylinder, which concrete layer includes the wire mesh disposed therein. A temporary layer of plastic material may be wrapped around the concrete layer to preserve the moisture content in the concrete to facilitate curing of the concrete, which plastic material is removed before the concrete-coated steel pipe is placed into service.
While such conventional concrete-coated steel pipes are capable of providing some degree of corrosion protection to the underlying steel cylinder, the level of corrosion protection will vary depending on the rate of chloride, moisture and oxygen diffusion through the concrete layer. The rate of chloride, moisture and oxygen diffusion through the concrete layer can vary depending on such factors as the thickness of the concrete layer, the specific formulation of the concrete layer, and the integrity of the concrete layer itself. For example, a concrete layer having cracks or other structural defects, e.g., caused when made, when transported, or when placed in certain end-use services or applications, will provide a high level of chloride, moisture and oxygen diffusion, thereby offering a low level of corrosion resistance to the underlying steel cylinder that will adversely effect service life. Another example is that of the concrete being subjected to cyclic wetting with chloride-containing water, then drying. Such cyclic wetting and drying will concentrate chlorides near the steel surface, and pump oxygen through the concrete, the combined action of which will eventually negate the passivating effect of high-pH concrete on steel and cause the steel to corrode.
It is, therefore, desired that an improved pipe be developed that is capable of being used in place of conventional concrete-coated steel pipe, and that is engineered to provide an improved degree of corrosion resistance when placed into typical end-use applications. It is also desired that such improved pipe be engineered in a manner that provides an improved degree of crack propagation resistance, to thereby both ensure the structural stability of the pipe and to operate as an additional mechanism to provide improved corrosion resistance. It is further desired that such improved pipe be manufactured in a manner that is efficient and cost effective.